Unicode in Erlang logs with logger - unicode

Question

I’m trying to output some Unicode into log with:
logger:debug("~ts", [<<"Тест"/utf8>>]).
and getting the following in log:
DEFAULT FORMATTER CRASHEDDEFAULT FORMATTER CRASHEDDEFAULT FORMATTER....
However, if I use ~s as a format string instead, it doesn’t crash, but outputs non-unicode version:
debug: ТеÑ<U+0081>Ñ<U+0082>
Any ideas? Can’t seem to find what am I doing wrong.
Environment
Erlang/OTP 21 [erts-10.0.5] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]
Logger config from sys.config:
{kernel, [
{logger, [
{handler, default, logger_std_h,
#{level => debug,
formatter => {logger_formatter, #{single_line => true}},
config => #{type => {file, "log/main.log"}}}},
{handler, errors, logger_std_h,
#{level => error,
formatter => {logger_formatter, #{single_line => false}},
config => #{type => {file, "log/errors.log"}}}}
]},
{logger_level, debug}
]}

Answer 1

I spent whole night tracing with someone on Erlang Slack channel and we found that it is single line formatter specifically that had a bug crashing the whole thing. It's now fixed in 21.1. After upgrading the issue's gone.